This proposed project seeks to develop the recent paradigm that protein complexes can be multi-configurational, if not highly dynamic entities. The biophysical and functional features of such dynamic complexes need to be understood. We chose heterodimer complexes involving Eph-family SAM domains as an example. SAM domains are important as they occur in over 200 human proteins, most notably in all 14 members of human Eph receptor tyrosine kinases. These receptors function in the development of the nervous and cardiovascular systems, and recent studies have shown that the SAM domain of EphA2 is mutated in a variety of human tumors as well as cataract, both linked to EphA2 dysregulation. However, the molecular basis of the normal and abnormal function of EphA2 SAM domain is not yet understood. Using a three-pronged approach, involving biophysical, computational and cell biology methods we will characterize the multi-configurational features of EphA1-SHIP2 and EphA2-SHIP2 SAM:SAM complexes. Furthermore, we will study how tumor associated mutations affect not just protein folding, stability and aggregation, but likely affect SAM domain-protein interactions via alterations of the configurational and internal dynamics of SAM domains. We will study the effect of specific tyrosine phosphorylation in the same manner, revealing the molecular basis of these functionally important posttranslational modifications. Investigations of Eph-related SAM domain conformational dynamics and protein-protein interactions have shifted our perspective on the normal and disease function of the domain. The knowledge obtained from this basic science research will serve as a general model for other dynamic protein complexes. Furthermore, the insights obtained, may eventually lead to the design of diagnostic and therapeutic agents.